Hydrocarbons, and other fluids, are often contained within subterranean formations at elevated pressures. Wells drilled into these formations allow the elevated pressure within the formation to force the fluids to the surface. However, in low pressure formations, or when the formation pressure has diminished, the formation pressure may be insufficient to force the fluids to the surface. In these cases, a pump may be installed to provide the required pressure to produce the fluids.
The volume of well fluids produced from a low pressure well is often limited, thus limiting the potential income generated by the well. For wells that require pumping systems, the installation and operating costs of these systems often determine whether a pumping system is installed to enable production or the well is abandoned. Among the more significant costs associated with pumping systems are the costs for installing, maintaining, and powering the system. Reducing these costs may allow more wells to be produced economically and increase the efficiency of wells already having pumping systems.
In recent years, the deployment of small diameter pumps in the production tubing has often provided for economic recovery of well bore fluids. One example of such a small diameter pump is disclosed in commonly assigned U.S. Pat. No. 7,252,148. Commercially available small diameter pumps are commonly powered via hydraulic actuation and are therefore connected to the surface via one or more hydraulic lines. For example, the hydraulic actuation may be configured to drive a piston in the diaphragm chamber of a diaphragm pump. Reciprocation of the piston is commonly accomplished via a switching mechanism having first and second states. In the first state, the fluid porting is such that the piston is extended. In the second state, the fluid porting is changed so as to cause retraction of the piston. One such switching mechanism is disclosed in commonly assigned, co-pending U.S. Patent Publication 2008/0003118.
While hydraulically actuated submersible pumps have been commercially utilized, they have been known on occasion to become hydraulically locked in service. Such hydraulic locking sometimes results in the need to remove the pump from the wellbore. Therefore, a need remains for an improved hydraulically actuated semisubmersible pump.